U.S. patent number 7,706,156 [Application Number 11/809,465] was granted by the patent office on 2010-04-27 for resonant converter with synchronous rectification drive circuit.
This patent grant is currently assigned to Tung Nan Institute of Technology. Invention is credited to Guan-Chyun Hsieh, Wei-Li Hsu, Cheng-Yuan Tsai.
United States Patent |
7,706,156 |
Hsieh , et al. |
April 27, 2010 |
Resonant converter with synchronous rectification drive circuit
Abstract
The present invention provides a resonant converter with a
synchronous rectification drive circuit. The resonant converter
with the synchronous rectification drive circuit includes a switch
circuit, a resonant circuit, a transformer, a full-wave-rectifier
circuit and a synchronous rectification drive circuit, wherein the
switch circuit at least includes a half-bridge circuit, the
resonant circuit is coupled to the switch circuit and has a
resonant frequency, the transformer has a primary side coupled to
the resonant circuit, the full-wave-rectifier circuit is coupled to
a secondary side of the transformer and includes two switches, the
synchronous rectification drive circuit includes four
voltage-clamped drive circuits having output terminals coupled to
the switch circuit and the corresponding switch of the
full-wave-rectifier circuit, and each voltage-clamped drive circuit
includes a transmission/discharge circuit for reducing the turn-off
period of the coupled switch during turning off the coupled
switch.
Inventors: |
Hsieh; Guan-Chyun (Taipei,
TW), Hsu; Wei-Li (Taipei, TW), Tsai;
Cheng-Yuan (Taipei, TW) |
Assignee: |
Tung Nan Institute of
Technology (Taipei, TW)
|
Family
ID: |
39526954 |
Appl.
No.: |
11/809,465 |
Filed: |
June 1, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080144339 A1 |
Jun 19, 2008 |
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Foreign Application Priority Data
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Dec 14, 2006 [TW] |
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95146949 A |
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Current U.S.
Class: |
363/21.02 |
Current CPC
Class: |
H02M
3/33592 (20130101); H02M 1/08 (20130101); H02M
1/0058 (20210501); Y02B 70/10 (20130101) |
Current International
Class: |
H02M
3/335 (20060101) |
Field of
Search: |
;363/21.02,21.06,15-17,98,126,127 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Berhane; Adolf
Assistant Examiner: Mehari; Yemane
Attorney, Agent or Firm: Haverstock & Owens LLP
Claims
What is claimed is:
1. A resonant converter with a synchronous rectification drive
circuit, comprising: a switch circuit including at least one bridge
arm having a first switch and a second switch; a resonant circuit
coupled to the switch circuit and having a resonant frequency; a
transformer having a primary side coupled to the resonant circuit
and having a secondary side; a full-wave-rectifier circuit coupled
to the secondary side and including a third switch and a fourth
switch; and a synchronous rectification drive circuit including a
first, a second, a third and a fourth voltage-clamped drive
circuits, wherein output terminals of the voltage-clamped drive
circuits are respectively coupled to the first, the second, the
third and the fourth switches, and each of the voltage-clamped
drive circuits includes a transmission/discharge circuit for
reducing a turn-off period of the coupled switches during turning
off the coupled switches.
2. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, wherein the switch circuit is one
of a half-bridge circuit and a full-bridge circuit, and each of the
first switch and the second switch is a power transistor including
a main body, a body-diode and a parasitic junction capacitor.
3. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, wherein the resonant circuit
includes a resonant capacitor, a resonant inductor and a
magnetizing inductor in series.
4. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, wherein each of the third switch
and the fourth switch is a power transistor including a main body
and a body-diode.
5. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, wherein each of the
voltage-clamped drive circuits includes: a clamp circuit changing
an AC drive signal into a DC drive signal; and the
transmission/discharge circuit coupled to the clamp circuit and
having an output terminal coupled to one of the first switch, the
second switch, the third switch and the fourth switch for forming
one of a first switch drive signal, a second switch drive signal, a
third switch drive signal and a fourth switch drive signal.
6. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, further comprising: a first drive
transformer having a first primary side winding set and two first
secondary side winding sets, wherein the first primary side winding
set is connected to a first couple capacitor in series for
receiving a first phase signal, and the first secondary side
winding sets are coupled to the first voltage-clamped drive circuit
and the fourth voltage-clamped drive circuit, respectively; and a
second drive transformer having a second primary side winding set
and two second secondary side winding sets, wherein the second
primary winding set is connected to a second couple capacitor in
series for receiving a second phase signal, and the second
secondary side winding sets are coupled to the second
voltage-clamped drive circuit and the third voltage-clamped drive
circuit, respectively.
7. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, further comprising: a first
isolator having a first input terminal coupled to a drive signal
producing device for receiving a first phase signal and having a
first output terminal coupled to the fourth voltage-clamped drive
circuit for preventing the first phase signal from being interfered
by a first signal from the fourth voltage-clamped drive circuit;
and a second isolator having a second input terminal coupled to the
drive signal producing device for receiving a second phase signal
and having a second output terminal coupled to the third
voltage-clamped drive circuit for preventing the second phase
signal from being interfered by a second signal from the third
voltage-clamped drive circuit.
8. The resonant converter with a synchronous rectification drive
circuit according to the claim 1, wherein the voltage-clamped drive
circuits respectively provide a first, a second, a third and a
fourth switch drive signals according to an operation switching
frequency and the resonant frequency of the resonant converter for
respectively driving the switches.
9. The resonant converter with a synchronous rectification drive
circuit according to the claim 5, wherein the clamp circuit
includes: a clamp capacitor; and a clamp diode.
10. The resonant converter with a synchronous rectification drive
circuit according to the claim 5, wherein the
transmission/discharge circuit includes: a transmission diode
passing the DC drive signal therethrough; and a discharge
transistor coupled to the clamp circuit, the transmission diode and
the coupled switches for accelerating a discharge path during
turning off the coupled switches.
11. The resonant converter with a synchronous rectification drive
circuit according to the claim 7, wherein each of the first
isolator and the second isolator is a drive transformer.
12. The resonant converter with a synchronous rectification drive
circuit according to the claim 7, wherein each of the first
isolator and the second isolator is an optical coupler.
13. The resonant converter with a synchronous rectification drive
circuit according to the claim 8, wherein as the operation switch
frequency is higher than the resonant frequency, the first switch
drive signal is identical to the fourth switch drive signal, the
second switch drive signal is identical to the third switch drive
signal, and the first switch drive signal and the second switch
drive signal are alternately produced.
Description
FIELD OF THE INVENTION
This invention relates to a resonant circuit with a synchronous
rectification drive circuit, and more particular to an LLC series
resonant converter in a power supply.
BACKGROUND OF THE INVENTION
Recently, the trend of the electronic equipments is toward the
application with low voltage and high current. The power management
technology is developed from the rectification of the rectification
diode to the synchronous rectification of the
metal-oxide-semiconductor field-effect transistor (MOSFET). The
power consumed in the equipment with the rectification diode is
more than that consumed in the equipment with the MOSFET; moreover,
the performance of the switching power supply can be increased by
the latter. The MOSFET is used for the power supply of the LCD TV
with low noise and high efficiency and for the power supply of the
computer and the telecommunication equipments.
Please refer to FIG. 1(a) showing the circuit of the rectification
diode typed LLC series resonant converter in the prior art. The LLC
series resonant converter 10 includes a switch circuit 21, a
resonant circuit 22, a transformer 23 and a full-wave-rectifier
circuit 24.
In FIG. 1(a), the switch circuit 21 is composed of a first switch
211 and a second switch 212, wherein the first switch 211 is
composed of a main body Q.sub.1 of a first power transistor, a
first body-diode D.sub.B1 and a first parasitic junction capacitor
C.sub.O1, and the second switch 212 is composed of a main body
Q.sub.2 of a second power transistor, a second body-diode D.sub.B2
and a second parasitic junction capacitor C.sub.O2. The first
switch 211 is connected to the second switch 212 to form a
half-bridge circuit. In addition, the switch circuit 21 can be a
full-bridge circuit. The resonant circuit 22 is composed of a
resonant inductor L.sub.r, a resonant capacitor C.sub.r and a
magnetizing inductor L.sub.m. It is known by one skilled in the art
that the resonant inductor L.sub.r can be composed of a leakage
inductor of the transformer 23.
As shown in FIG. 1(a), there is a DC voltage source V.sub.DC for
the switch circuit 21 to provide an output voltage V.sub.o on a
load R.sub.L via the resonant circuit 22, the transformer 23, the
full-wave-rectifier circuit 24 and a voltage stabilizing capacitor
C.sub.L. The switch 21 is separated from the resonant circuit 22
and the full-wave-rectifier circuit 24 by the transformer 23 via a
primary side winding set N.sub.p and series connected secondary
side winding sets N.sub.S1 and N.sub.S2. The full-wave-rectifier
circuit 24 is composed of a first rectification diode D.sub.1 and a
second rectification diode D.sub.2 connected to the voltage
stabilizing C.sub.L. The anode of the first rectification diode
D.sub.1 is connected to the positive dotted terminal of the
secondary side winding set N.sub.S1, and the anode of the second
rectification diode D.sub.2 is connected to the negative dotted
terminal of the secondary side winding set N.sub.S2. The junction
of the secondary side winding sets N.sub.S1 and N.sub.S2 is used as
the ground end of the output voltage V.sub.o, and the cathodes of
the rectification diodes D.sub.1 and D.sub.2 are used as the high
voltage end of the output voltage V.sub.o.
Please refer to FIG. 1(b) showing the frequency responses of the
resonant converter shown in FIG. 1(a) with various circuit quality
factors. As shown in FIG. 1(b), the circuit quality factor Q.sub.K
is related to the load R.sub.L and the magnetizing current i.sub.m,
wherein K=Lm/Lr, and the LLC series resonant converter 10 is
equivalent to an LC series resonant converter when K approximates
to infinity.
As shown in FIG. 1(b), there are a first resonant frequency
f.sub.r1 and a second resonant frequency f.sub.r2. The first
resonant frequency f.sub.r1 is related to the resonant inductor
L.sub.r and the resonant capacitor C.sub.r, the second resonant
frequency f.sub.r2 is related to the resonant inductor L.sub.r, the
magnetizing inductor L.sub.m and the resonant capacitor C.sub.r,
and the relationships thereamong are as follows. f.sub.r1=1/(2.pi.
{square root over (L.sub.rC.sub.r)}) f.sub.r2=1/(2.pi. {square root
over (L.sub.m+L.sub.r)C.sub.r)})
As shown in FIG. 1(b), there are three operation frequency regions
demarcated by the first resonant frequency f.sub.r1 and the second
resonant frequency f.sub.r2. The operation switching frequency fs
corresponding to the first frequency region Region-1 has the
relationship as f.sub.s>f.sub.r1. The operation switching
frequency fs corresponding to the second frequency region Region-2
has the relationship as f.sub.r2<f.sub.s<f.sub.r1. The
operation switching frequency fs corresponding to the third
frequency Region-3 has the relationship as f.sub.s<f.sub.r2. In
order to achieve the zero voltage switching and the wide range of
voltage stabilization, the first frequency region Region-1 and the
second frequency region Region-2 are first considered to be used
for the LLC series resonant converter 10; however, in order to
achieve the zero voltage switching of the first switch 211 and the
second switch 212 and to facilitate the design of the drive
circuit, it is well known to use the second frequency region
Region-2.
Please refer to FIG. 1(c) showing signals of the resonant converter
shown in FIG. 1(a), which operates in the second frequency region.
In FIG. 1(c), there are a first switch drive signal V.sub.GS1, a
second switch drive signal V.sub.GS2, a resonant current i.sub.L, a
magnetizing current i.sub.m, a power transfer current i.sub.p and a
periodic change of a resonant capacitor voltage drop V.sub.Cr
operating in the second frequency region Region-2, wherein the
power transfer current i.sub.p is zero at t.sub.0, t.sub.1, t.sub.2
and t.sub.3, there is zero voltage switching on the main body
Q.sub.1 of the first power transistor and the main body Q.sub.2 of
the second power transistor at the dead periods of t.sub.1-t.sub.3
and t.sub.4-t.sub.6, and the magnetizing current i.sub.m at the
periods is approximately a constant.
Please refer to FIG. 1(d) showing signals of the resonant converter
shown in FIG. 1(a), which operates in the first frequency region.
In FIG. 1(d), there are a first switch drive signal V.sub.GS1, a
second switch drive signal V.sub.GS2, a resonant current i.sub.L, a
magnetizing current i.sub.m, a power transfer current i.sub.p and a
periodic change of a resonant capacitor voltage drop V.sub.Cr
operating in the first frequency region Region-1, wherein the main
body Q.sub.1 of the first power transistor and the main body
Q.sub.2 of the second power transistor are respectively turned off
at t.sub.1 and t.sub.4; thereupon the power transfer current
i.sub.p is gradually decreased, and the energy is continuously
transferred to the load. Therefore, the magnetizing current i.sub.m
is continuously and linearly increased until the main body of the
next power transistor is electrified, and the power transfer
current i.sub.p is zero at t.sub.3 and t.sub.6. The zero voltage
switching on the main boy Q.sub.1 of the first power transistor and
the main body Q.sub.2 of the second power transistor is maintained
due to the magnetizing current i.sub.m with the triangular
waveform.
In FIGS. 1(c) and 1(d), the LLC series resonant converter 10 is
practiced by using the rectification diode. However, under the
identical conditions, the operation of the LLC series resonant
converter in the second frequency region Region-2 fails if the LLC
series resonant converter uses the MOSFET as the rectification
switch.
Please refer to FIG. 2 showing the circuit of the synchronous
rectification typed LLC series resonant converter in the prior art.
FIG. 1(a) is compared with FIG. 2. The first rectification diode
D.sub.1 and the second rectification diode D.sub.2 shown in FIG.
1(a) are replaced with the third switch 243 and the fourth switch
244, respectively, and the connection of the high voltage end of
the output part and the ground end is changed so as to form the
circuit shown in FIG. 2. It means that the third switch 243 is
composed of a main body Q.sub.3 of a third power transistor and a
third body-diode D.sub.B3, and the fourth switch 244 is composed of
the main body Q.sub.4 of the fourth power transistor and the fourth
body-diode D.sub.B4. The main bodies Q.sub.3 and Q.sub.4 of the
power transistors have sources connected to the ground end of the
output voltage V.sub.o. The main body Q.sub.3 of the third power
transistor has a drain connected to the positive dotted terminal of
the secondary side winding set N.sub.S1. The main body Q.sub.4 of
the fourth power transistor has a drain connected to the negative
dotted terminal of the secondary side winding set N.sub.S2. In
addition, the fourth switch rectification current i.sub.Q4 flows
into the negative dotted terminal of the secondary side winding set
N.sub.S2, and the third switch rectification current i.sub.Q3 flows
into the positive dotted terminal of the secondary side winding set
N.sub.S1.
The operation of the synchronous rectification typed LLC series
resonant converter 40 in the second frequency region Region-2 is
illustrated as follows. It is set that the first switch drive
signal V.sub.GS1 is identical to the fourth switch drive signal
V.sub.GS4, the second switch drive signal V.sub.GS2 is identical to
the third switch drive signal V.sub.GS3, and the switch drive
signals are identical to those in FIG. 1(c). There is the current
through one of the third body-diode D.sub.B3 and the fourth
body-diode D.sub.B4 at the dead periods of t.sub.1-t.sub.3 and
t.sub.4-t.sub.6, so as to transfer the power from the secondary
side to the primary side of the transformer 23, and therefore the
circuit cannot operate normally and safely.
When the synchronous rectification typed LLC series resonant
converter operates in the first frequency region Region-1, the
converter operates normally due to the magnetizing current i.sub.m
with the triangular waveform.
If the conventional synchronous rectification typed LLC series
resonant converter 40 shown in FIG. 2 operates in the second
frequency region Region-2, there must be different pulse widths for
the first switch drive signal V.sub.GS1 and the fourth switch drive
signal V.sub.GS4. Similarly, there must be different pulse widths
for the second switch drive signal V.sub.GS2 and the third switch
drive signal V.sub.GS3.
In order to practice the operations in the first frequency region
Region-1 and the second frequency region Region-2 for the
conventional synchronous rectification drive circuit, the drive
circuit is quite complicated. Therefore, the cost is high and the
energy is wasted owing to ignoring to increase the conversion
efficiency.
Accordingly, the drive circuit of the synchronous rectification
typed LLC series resonant converter should be simplified to reduce
the volume of the circuit, so as to lower the cost and to achieve
high efficiency and low noise.
In order to overcome the disadvantages of the prior art described
above, the present invention provides a resonant converter with a
synchronous rectification drive circuit.
SUMMARY OF THE INVENTION
It is an aspect of the present invention to provide a resonant
converter with a synchronous rectification drive circuit including
a switch circuit, a resonant circuit, a transformer, a
full-wave-rectifier circuit and a synchronous rectification drive
circuit, wherein the synchronous rectification drive circuit
includes four voltage-clamped drive circuits respectively coupled
to the switch circuit and the full-wave-rectifier circuit, and each
voltage-clamped drive circuit includes a clamp circuit and a
transmission/discharge circuit for reducing the turn-off period of
the switch, so as to increase the efficiency of the resonant
converter when the switch circuit and the full-wave-rectifier
circuit are turned off.
It is another aspect of the present invention to provide a resonant
converter with a synchronous rectification drive circuit, wherein
there are four voltage-clamped drive circuits divided into two
groups, and the two groups are respectively driven to alternately
provide identical switch drive signals, so that the resonant
converter has an operation switching frequency higher than a
resonant frequency thereof for the conversion performance on the
wide range of the voltage regulation.
In accordance with the present invention, the resonant converter
with a synchronous rectification drive circuit includes a switch
circuit having at least one bridge arm having a first switch and a
second switch; a resonant circuit coupled to the switch circuit and
having a resonant frequency; a transformer having a primary side
coupled to the resonant circuit and a secondary side; a
full-wave-rectifier circuit coupled to the secondary side and
having a third switch and a fourth switch; and a synchronous
rectification drive circuit having a first voltage-clamped drive
circuit, a second voltage-clamped drive circuit, a third
voltage-clamped drive circuit and a fourth voltage-clamped drive
circuit, wherein output terminals of the voltage-clamped drive
circuits are coupled to the first switch, the second switch, the
third switch and the fourth switch, respectively, and each of the
voltage-clamped drive circuits includes a transmission/discharge
circuit for reducing a turn-off period of the coupled switches
during turning off the coupled switches.
In accordance with the present invention, the switch circuit is one
of a half-bridge circuit and a full-bridge circuit, and each of the
first switch and the second switch is a power transistor including
a main body, a body-diode and a parasitic junction capacitor.
In accordance with the present invention, the resonant circuit
includes a resonant capacitor, a resonant inductor and a
magnetizing inductor in series.
In accordance with the present invention, each of the third switch
and the fourth switch is a power transistor including a main body
and a body-diode.
In accordance with the present invention, each of the
voltage-clamped drive circuits includes a clamp circuit changing an
AC drive signal into a DC drive signal, and includes the
transmission/discharge circuit coupled to the clamp circuit and
having an output terminal coupled to one of the first switch, the
second switch, the third switch and the fourth switch for providing
one of a first switch drive signal, a second switch drive signal, a
third switch drive signal and a fourth switch drive signal.
In accordance with the present invention, the clamp circuit
includes a clamp capacitor and a clamp diode.
In accordance with the present invention, the
transmission/discharge circuit includes a transmission diode
passing the DC drive signal therethrough, and includes a discharge
transistor coupled to the clamp circuit, the transmission diode and
the coupled switches for accelerating a discharge path during
turning off the coupled switches.
In accordance with the present invention, the resonant converter
with a synchronous rectification drive circuit includes a first
drive transformer having a first primary side winding set and two
first secondary side winding sets, wherein the first primary side
winding set is connected to a first couple capacitor in series for
receiving a first phase signal, and the first secondary side
winding sets are respectively coupled to the first voltage-clamped
drive circuit and the fourth voltage-clamped drive circuit, and the
resonant converter with a synchronous rectification drive circuit
further includes a second drive transformer having a second primary
side winding set and two second secondary side winding sets,
wherein the second primary winding set is connected to a second
couple capacitor in series for receiving a second phase signal, and
the second secondary side winding sets are respectively coupled to
the second voltage-clamped drive circuit and the third
voltage-clamped drive circuit.
In accordance with the present invention, the resonant converter
with a synchronous rectification drive circuit includes a first
isolator having a first input terminal coupled to a drive signal
producing device for receiving a first phase signal and having a
first output terminal coupled to the fourth voltage-clamped drive
circuit for preventing the first phase signal from being interfered
by a first signal from the fourth voltage-clamped drive circuit,
and the resonant converter with a synchronous rectification drive
circuit further includes a second isolator having a second input
terminal coupled to the drive signal producing device for receiving
a second phase signal and having a second output terminal coupled
to the third voltage-clamped drive circuit for preventing the
second phase signal from being interfered by a second signal from
the third voltage-clamped drive circuit.
In accordance with the present invention, each of the first
isolator and the second isolator is a drive transformer or an
optical coupler.
In accordance with the present invention, the voltage-clamped drive
circuits respectively provide a first, a second, a third and a
fourth switch drive signals according to an operation switching
frequency and the resonant frequency of the resonant converter for
respectively driving the switches.
In accordance with the present invention, as the operation switch
frequency is higher than the resonant frequency, the first switch
drive signal is identical to the fourth switch drive signal, the
second switch drive signal is identical to the third switch drive
signal and, the first switch drive signal and the second switch
drive signal are alternately produced.
The above aspects and advantages of the present invention will
become more readily apparent to those ordinarily skilled in the art
after reviewing the following detailed description and accompanying
drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) shows a circuit of a rectification diode typed LLC series
resonant converter in the prior art.
FIG. 1(b) is a diagram showing the frequency response of the
resonant converter shown in FIG. 1(a) with various circuit quality
factors.
FIG. 1(c) is a diagram showing signals of the resonant converter
shown in FIG. 1(a) operated in a second frequency region.
FIG. 1(d) is a diagram showing signals of the resonant converter
shown in FIG. 1(a) operated in a first frequency region.
FIG. 2 is a circuit of a synchronous rectification typed LLC series
resonant converter in the prior art.
FIG. 3 shows a circuit of a resonant converter with a synchronous
rectification drive circuit according to a preferred embodiment of
the present invention.
FIG. 4 shows a first preferred embodiment of the synchronous
rectification drive circuit according to the present invention.
FIG. 5 shows a second preferred embodiment of the synchronous
rectification drive circuit according to the present invention.
FIG. 6(a) shows signals of the resonant converter shown in FIG. 3
and FIG. 4 according to the present invention.
FIG. 6(b) shows signals of the resonant converter shown in FIG. 3
and FIG. 4 according to the present invention.
FIG. 6(c) shows signals presenting the zero voltage switching of
the resonant converter shown in FIG. 3 and FIG. 4 according to the
present invention.
FIG. 7 is a diagram showing the comparison of the power efficiency
between the resonant converter shown in FIG. 1 and the resonant
converter of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention is described more specifically with reference to the
following embodiments. It is to be noted that the following
descriptions of preferred embodiments of this invention are
presented herein for the purpose of illustration and description
only; it is not intended to be exhaustive or to be limited to the
precise form disclosed.
Please refer to FIG. 3 showing a resonant converter with a
synchronous rectification drive circuit according to a preferred
embodiment of the present invention. In the figures, similar
components are denoted as similar reference numbers. It is to be
noted that a switch circuit 21 of an input terminal is composed of
a half-bridge circuit having a bridge arm in FIG. 3. Alternatively,
the switch circuit 21 of the input terminal can be composed of a
full-bridge circuit having two bridge arms. The resonant converter
60 has a synchronous rectification drive circuit 25 for
implementing the synchronous rectification drive of the present
invention. In addition, power transistors are used as the switches
in the embodiment of the present invention; however, the term
"switch" claimed in the present invention is not limited to the
power transistor.
As shown in FIG. 3, the synchronous rectification drive circuit 25
includes a first voltage-clamped drive circuit 251, a second
voltage-clamped drive circuit 252, a third voltage-clamped drive
circuit 253 and a fourth voltage-clamped drive circuit 254. The
first voltage-clamped drive circuit 251 has an input terminal for
receiving a first AC drive signal v.sub.H1, and has an output
terminal coupled to the first switch 211 for providing a first
switch drive signal v.sub.GS1 to control turn on/off of the first
switch 211. The second voltage-clamped drive circuit 252 has an
input terminal for receiving a second AD drive signal v.sub.H2, and
has an output terminal coupled to the second switch 212 for
providing a second switch drive signal v.sub.GS2 to control turn
on/off of the second switch 212. The third voltage-clamped drive
circuit 253 has an input terminal for receiving a third AD drive
signal v.sub.H3, and has an output terminal coupled to the third
switch 243 for providing a third switch drive signal v.sub.GS3 to
control turn on/off of the third switch 243. The fourth
voltage-clamped drive circuit 254 has an input terminal for
receiving a fourth AD drive signal v.sub.H4, and has an output
terminal coupled to the fourth switch 244 for providing a fourth
switch drive signal v.sub.GS4 to control turn on/off of the fourth
switch 244.
As above illustrations, when the resonant converter 60 has an
operation switching frequency f.sub.s higher than a resonant
frequency f.sub.r1 thereof, i.e. the resonant converter 60 operates
in a first frequency region Region-1, it is set that the first
switch drive signal v.sub.GS1 is identical to the fourth switch
drive signal v.sub.GS4, the second switch drive signal v.sub.GS2 is
identical to the third switch drive signal v.sub.GS3, and the first
switch drive signal v.sub.GS1 and the second switch drive signal
v.sub.GS2 are alternately produced. When the resonant converter 60
operates in the second frequency region Region-2, there must be
different pulse widths for the first switch drive signal v.sub.GS1
and the fourth switch drive signal v.sub.GS4. Similarly, there must
be different pulse widths for the second switch drive signal
v.sub.GS2 and the third switch drive signal v.sub.GS3. As shown in
FIG. 3, the sequence of the first AC drive signal v.sub.H1, the
second AC drive signal v.sub.H2, the third AC drive signal v.sub.H3
and the fourth AC drive signal v.sub.H4 can be regulated for
various synchronous rectification drive conditions. In order to
illustrate the practice of the synchronous rectification drive
circuit of the present invention, the following embodiments of two
synchronous rectification drive circuits 25 are provided to show
the arrangement of the synchronous rectification drive circuit 25
when the resonant converter 60 operates in the first frequency
region Region-1.
Please refer to FIG. 4 showing a synchronous rectification drive
circuit according to the first preferred embodiment of the present
invention. Each of a first voltage-clamped drive circuit 251, a
second voltage-clamped drive circuit 252, a third voltage-clamped
drive circuit 253 and a fourth voltage-clamped drive circuit 254 of
the synchronous rectification drive circuit 25 includes a clamp
circuit 301 and a transmission/discharge circuit 302. In the first
voltage-clamped drive circuit 251, the clamp circuit 301 is used
for raising the first AC drive signal v.sub.H1 to a first DC drive
signal v.sub.K1, the transmission/discharge circuit 302 is coupled
to the clamp circuit 301, and an output terminal is coupled to the
first switch 211 for receiving a first DC drive signal v.sub.K1 to
provide the first switch drive signal v.sub.GS1. In the second
voltage-clamped drive circuit 252, the clamp circuit 301 is used
for raising the second AC drive signal v.sub.H2 to a second DC
drive signal v.sub.K2, the transmission/discharge circuit 302 is
coupled to the clamp circuit 301, and an output terminal is coupled
to the second switch 212 for receiving a second DC drive signal
v.sub.K2 to provide the second switch drive signal v.sub.GS2. In
the third voltage-clamped drive circuit 253, the clamp circuit 301
is used for raising the third AC drive signal v.sub.H3 to a third
DC drive signal v.sub.K3, the transmission/discharge circuit 302 is
coupled to the clamp circuit 301, and an output terminal is coupled
to the third switch 213 for receiving a third DC drive signal
v.sub.K3 to provide the third switch drive signal v.sub.GS3. In the
fourth voltage-clamped drive circuit 254, the clamp circuit 301 is
used for raising the fourth AC drive signal v.sub.H4 to a fourth DC
drive signal v.sub.K4, the transmission/discharge circuit 302 is
coupled to the clamp circuit 301, and an output terminal is coupled
to the fourth switch 214 for receiving a fourth DC drive signal
v.sub.K4 to provide the fourth switch drive signal v.sub.GS4.
Each clamp circuit 301 includes a clamp capacitor C.sub.A1 and a
clamp diode D.sub.E1. The transmission/discharge circuit 302
includes a transmission diode D.sub.E2 and a discharge transistor
Q.sub.5. The transmission diode D.sub.E2 is used for passing
corresponding DC drive signal therethrough, i.e. when the raising
edge of the corresponding DC drive signal is received by the
transmission diode D.sub.E2, an input gate capacitor of the coupled
switch is charged. The input gate capacitor is composed of a
gate-drain capacitor C.sub.GD and a gate-source capacitor C.sub.GS.
When the charging voltage of the gate-source capacitor C.sub.GS is
higher than the conducting voltage of the coupled switch, the
coupled switch is electrically connected. The discharge transistor
Q.sub.5 is coupled to the clamp circuit 301, the transmission diode
D.sub.E2 and the coupled switch for accelerating a discharge path
during turning off the coupled switch, i.e. when the falling edge
of the corresponding DC drive signal is received by the
transmission diode D.sub.E2 and the discharge transistor Q.sub.5,
the discharge transistor Q.sub.5 is electrically connected, and
store charges of the input gate capacitor are discharged via the
discharge transistor Q.sub.5, so that the turn-off period of the
coupled switch is reduced. Accordingly, it is advantageous to the
sequential control of the synchronous rectification drive circuit
25 and raising the power efficiency.
As shown in FIG. 4, the synchronous rectification drive circuit 25
further includes a first drive transformer 255 and a second drive
transformer 256. The first drive transformer 255 has a primary side
winding set N.sub.PA and two secondary side winding sets N.sub.SA1
and N.sub.SA2. The primary side winding set N.sub.PA is connected
to a first couple capacitor C.sub.S1 for receiving a first phase
signal v.sub.S1. The DC part of the first phase signal v.sub.S1
would not be transmitted to the primary side winding set N.sub.PA
of the first drive transformer 255 due to the effect of the first
couple capacitor C.sub.S1. The secondary side winding set N.sub.SA1
is coupled to the first voltage-clamped drive circuit 251 for
providing the first AC drive signal v.sub.H1, and the secondary
side winding set N.sub.SA2 is coupled to the fourth voltage-clamped
drive circuit 254 for producing the fourth AC drive signal
v.sub.H4. The second drive transformer 256 has a primary side
winding set N.sub.PB and two secondary side winding sets N.sub.SB1
and N.sub.SB2. The primary side winding set N.sub.PB is connected
to a second couple capacitor C.sub.S2 for receiving a second phase
signal v.sub.S2. The DC part of the second phase signal v.sub.S
would not be transmitted to the primary side winding set N.sub.PB
of the second drive transformer 256 due to the effect of the second
couple capacitor C.sub.S2. The secondary side winding set N.sub.SB1
is coupled to the second voltage-clamped drive circuit 252 for
providing the second AC drive signal v.sub.H2, and the secondary
side winding set N.sub.SB2 is coupled to the third voltage-clamped
drive circuit 253 for producing the third AC drive signal
v.sub.H3.
Please refer to FIG. 5 showing a second preferred embodiment of the
synchronous rectification drive circuit according to the present
invention. As shown in FIG. 5, the synchronous rectification drive
circuit 25 includes a first phase drive circuit 25a and a second
phase drive circuit 25b. The first phase drive circuit 25a is
coupled to a drive signal producing device 26 for receiving a first
phase signal v.sub.S1, wherein the first phase signal v.sub.S1 is a
square waveform. The first phase signal v.sub.S1 is processed by
the first phase drive circuit 25a for providing the first switch
drive signal v.sub.GS1 and the fourth switch drive signal
v.sub.GS4, so as to drive the first switch 211 and the fourth
switch 244, respectively. The second phase drive circuit 25b is
coupled to a drive signal producing device 26 for receiving a
second phase signal v.sub.S2, wherein the second phase signal
v.sub.S2 is another square waveform. The second phase signal
v.sub.S2 is processed by the second phase drive circuit 25b for
providing the second switch drive signal v.sub.GS2 and the third
switch drive signal v.sub.GS3, so as to drive the second switch 212
and the third switch 243, respectively.
The first phase drive circuit 25a includes the first
voltage-clamped drive circuit 251, the fourth voltage-clamped drive
circuit 254 and a first isolator 257. Both the first
voltage-clamped drive circuit 251 and the first isolator 257 are
coupled to the drive signal producing device 26 for receiving a
first phase signal v.sub.S1. The first phase signal v.sub.S1 is
converted to the first switch drive signal v.sub.GS1 by the first
voltage-clamped drive circuit 251. The first isolator 257 can be a
drive transformer, an optical coupler or any other electrical
equipments with isolation functions. The first isolator 257 has an
output terminal coupled to the fourth voltage-clamped drive circuit
254 for preventing the first phase signal v.sub.S1 from being
interfered by signals of the fourth voltage-clamped drive circuit
254 from the load R.sub.L. The fourth AC drive signal v.sub.H4 is
produced by the first isolator 257. The fourth voltage-clamped
drive circuit 254 is coupled to the first isolator 257 for
receiving the fourth AC drive signal v.sub.H4 and converting the
fourth AC drive signal v.sub.H4 to the fourth switch drive signal
v.sub.GS4.
The first phase drive circuit 25b includes the second
voltage-clamped drive circuit 252, the third voltage-clamped drive
circuit 253 and a second isolator 258. Both the second
voltage-clamped drive circuit 252 and the second isolator 258 are
coupled to the drive signal producing device 26 for receiving a
second phase signal v.sub.S2. The second phase signal v.sub.S2 is
converted to the second switch drive signal v.sub.GS2 by the second
voltage-clamped drive circuit 252. The second isolator 258 can be a
drive transformer, an optical coupler or any other electrical
equipments with isolation functions. The second isolator 258 has an
output terminal coupled to the third voltage-clamped drive circuit
253 for preventing the second phase signal v.sub.S2 from being
interfered by signals of the third voltage-clamped drive circuit
253 from the load R.sub.L. The third AC drive signal v.sub.H3 is
produced by the second isolator 258. The third voltage-clamped
drive circuit 253 is coupled to the second isolator 258 for
receiving the third AC drive signal v.sub.H3 and converting the
third AC drive signal v.sub.H3 to the third switch drive signal
v.sub.GS3.
The drive circuit shown in FIG. 5 can be used in other converters
such as Boost typed, Buck typed and Buck-Boost typed
converters.
Please refer to FIG. 6(a) showing signals of the resonant converter
shown in FIG. 3 and FIG. 4 according to the present invention,
wherein the periodic changes of the first switch drive signal
v.sub.GS1, the second switch drive signal v.sub.GS2, the resonant
current i.sub.L and the resonant capacitance drop v.sub.Cr
operating in the first frequency region Region-1 are presented.
Please refer to FIG. 6(b) showing signals of the resonant converter
shown in FIG. 3 and FIG. 4 according to the present invention,
wherein the fourth switch drive signal v.sub.SG4, the second switch
drive signal v.sub.GS2, the fourth switch rectification current
i.sub.Q4 and the third switch rectification current i.sub.Q3 are
presented. Please refer to FIG. 6(c) showing signals presenting the
zero voltage switching of the resonant converter shown in FIG. 3
and FIG. 4 according to the present invention, wherein the zero
voltage switching of the first switch 211 is presented.
As shown in FIGS. 6(a)-6(c), when the resonant converter 60 has an
operation switching frequency f.sub.s higher than a resonant
frequency thereof, the first switch drive signal is identical to
the fourth switch drive signal, the second switch drive signal is
identical to the third switch drive signal, and the first switch
drive signal and the second switch drive signal are alternately
produced, the first switch and the second switch have the zero
voltage switching, the third switch and the fourth switch have the
zero voltage switching, and the third switch rectification current
and the fourth switch rectification current have the quasi-sine
waveform.
Please refer to FIG. 7 showing the comparison of the power
efficiency between the resonant converter shown in FIG. 1 and the
resonant converter of the present invention. As shown in FIG. 7,
the efficiency of the synchronous rectification resonant converter
is higher than that of the rectification diode resonant converter
when the output current is higher than 6 A, and the efficiency of
the synchronous rectification resonant converter approximates to
that of the rectification diode resonant converter when the output
current is lower than 6 A.
It is characterized in the present invention that a resonant
converter with a synchronous rectification drive circuit includes a
switch circuit, a resonant circuit, a transformer, a
full-wave-rectifier circuit and a synchronous rectification drive
circuit, wherein the switch circuit at least includes a half-bridge
circuit, the resonant circuit is coupled to the switch circuit and
has a resonant frequency, the transformer has a primary side
coupled to the resonant circuit, the full-wave-rectifier circuit is
coupled to a secondary side of the transformer and includes two
switches, the synchronous rectification drive circuit includes four
voltage-clamped drive circuits having output terminals coupled to
the switch circuit and the corresponding switch of the
full-wave-rectifier circuit, and each voltage-clamped drive circuit
includes a transmission/discharge circuit for reducing the turn-off
period of the coupled switch during turning off the coupled
switch.
While the invention has been described in terms of what is
presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention needs not be
limited to the disclosed embodiment. On the contrary, it is
intended to cover various modifications and similar arrangements
included within the spirit and scope of the appended claims which
are to be accorded with the broadest interpretation so as to
encompass all such modifications and similar structures.
* * * * *